The intermittent injection of a liquid that is to be vaporized may be carried out, for example, to achieve a constant mass flow and therewith a constant spatial distribution of the sprayed substance during a liquid delivery pulse. However, when a liquid injector is operated in such a pulsated or intermittent mode, after the end of each liquid pulse, it can occur that the pressure inside the space into which the liquid is sprayed, is lower than the vapor pressure of the injected liquid. This condition creates the danger that the liquid remaining in the discharge channel of the injector after the end of the liquid pulse may be vaporized. This can lead to a mixture of vapor and liquid coming out of the nozzle opening and forming drops of liquid on the nozzle. These drops are essentially ineffective, for example in achieving additional vaporization cooling, because they only wet a small area of the surface of a wall at which they are to be sprayed, or they remain directly near the nozzle opening. When these drops remain near the nozzle opening and vaporize there, it is likely that the liquid will freeze up near the nozzle opening, potentially plugging the nozzle unless auxiliary electrical heating elements are provided. However, providing electrical heaters would entail additional costs and efforts in manufacturing and operating the injector.
Furthermore, even with the provision of heaters, there would still be the disadvantage that the liquid coming out of the nozzle as unintended droplets cannot contribute to the intended heat exchange process or, that is to say, in the intended cooling effect. Thus, cooling liquid is wasted and the useable quantity of cooling liquid is reduced. This is especially disadvantageous in applications in the field of space travel, because maximum gross vehicle weights are strictly limited and any additional weight attributable to cooling liquid that will be wasted will directly reduce the allowable payload weight. Thus, the total relative costs of a space mission are increased.
Generally, it is known to use so-called vaporizing heat exchangers in a space vehicle to remove from the vehicle the waste heat generated, for example, by the electrical equipment on board. The removed heat is expelled into space outside the vehicle. Such vaporizing heat exchangers are described, for example, in the publication "Shuttle Orbiter Flash Evaporator", by J. R. Nason et al., Hamilton Standard, 79-ENAs-14, American Society of Mechanical Engineers (Editors). In these vaporizing heat exchangers a cooling fluid, which circulates through several active cooling circuits, is brought into thermic contact with a medium that is to be vaporized. This medium is sprayed as a jet of liquid drops through an injection nozzle into the operating space or working chamber of the heat exchanger. Thereby, the drops contact the walls bounding this working chamber, through which walls flows the above-mentioned cooling fluid. By absorbing heat from the chamber walls, and thereby extracting heat from the cooling fluid, the liquid drops transition into the vapor phase, whereupon the vapor is blown out of the spacecraft into space.